Bad Hesitation (video included) where should I start?

[96LX]

Last night I tested the TPS per the FSM, and it passed.

Then, I tried this test quick: https://forum.ih8mud.com/threads/fuel-pump-relay-and-resistor-the-60-second-test.95052/
The truck started up then almost stalled then fired back up, it did this a couple times before I turned it off. After thinking about it this test wasn't necessary with the symptoms I was having but I just want to document my procedure anyway.

At this point I was a bit exhausted of researching and diagnosing, so I took it for a drive to see if I could notice any patterns that might help the diagnosis. On the side streets it had its usual hesitation, I hit the highway and it was hesitating pretty good as I babied the throttle, a couple cars were approaching fast behind me, I went to accelerate hard and no acceleration was to be had, the rpms weren't climbing and neither was the speedometer, I just kept on the accelerator, I could hear whining which I am assuming was the fuel pump, this lasted for what seemed like 10 seconds but was probably more like 3 seconds. All of a sudden there was a huge surge of power and acceleration. I got up to speed, then got off the highway and tried my best to get it to stutter again, nothing.

I drove it to work this morning without the slightest hint that anything was ever wrong.

I don't really have an educated guess as to what was the cause or the fix, maybe it was bad fuel and I used the last of it? The tank is still 3/4 full though.

It was a grueling 3 days of diagnosis without any trails to follow, but I feel that I learned a lot about the systems of this truck. Thank you to everyone in this thread for sharing your knowledge!

If you have any guesses as to what it was, I am all ears!

 

[lumbee1]

How many miles have you driven it since the hesitation started?

 

[96LX]

There were about 50 highway miles between the first noticeable hesitation to arriving home from the trip with little to no hesitation inbetween. The next morning and following days I drove about 45 miles with lots of hesitation with acceleration and some at speed.

I have since driven 30 miles since it stopped and it seems completely back to normal

 

[wlittleman]

I had a similar problem, and am posting this same message on several similar threads as I solved my issue in a manner not described by any other post related to engine stumbling or hesitation.

These are the things I did (to no success)

• Added Chevron Techron fuel injector cleaner
• Replaced O2 sensors
• Checked O2 sensor connectors (they were wet and corroded, which fixed the Code 26 issue, but not the Code 71 issue)
• Replaced the engine coolant thermostat
• Replaced wires
• New plugs
• Replaced some of the vacuum lines
• New cap and rotor
• Checked both harness next to the EGR. Wire insulation was worn, but I covered it with silicone tape
• Checked wiring harness near ECU
• Installed new ECU
• Installed another working air flow meter
• Checked intake tube for cracks

The engine stumbling problem got more frequent and worse over a 4 year period. So, what fixed my problem? TIGHTENING THE VALVE COVER BOLTS!!!

Apparently, un-metered air was being brought into the engine via a leaking valve cover gasket. I only discovered this when I removed the oil filler cap while the engine was running, and it caused the engine to stumble and nearly die. The same would happen if I pull out the dip stick. After verifying that air was not leaking in through the oil filler cap or dip stick, I decided to check the valve cover bolts, and discovered 2 very loose bolts at the rear - they were so loose that I could spin them with my fingers. After tightening those bolts, resetting the ECU, letting the ECU go through the relearn/re-calibrate process, the engine ran smooth. I addition, the reoccurring code 71 never came back. It has been 3 months of problem free driving! I hope this helps the numerous folks with this similar problem.

 

[goneloco]

Just wondering if 96LX ever figured out this issue? Was it as simple as tightening the valve cover gaskets?

I am having the same issue, I believe, as you. Idles fine, when I accelerate using a lot of pedal it hesitates (does not run smooth). If I take off with minimal pedal it runs fine. Thanks

 

[96LX]

Just wondering if 96LX ever figured out this issue? Was it as simple as tightening the valve cover gaskets?

I am having the same issue, I believe, as you. Idles fine, when I accelerate using a lot of pedal it hesitates (does not run smooth). If I take off with minimal pedal it runs fine. Thanks

I did not tighten the bolts on the valve cover while this was happening like wlittleman did to fix his stumbling, it seems like an easy, worthwhile thing to check.

To this day I don't know what the cause was but now suspect it was bad fuel, because 7 years later I have not had the issue again.